The present invention relates to a new and improved fastener for use in retaining vertebrae in a desired spatial relationship.
Known fasteners have been used to retain vertebra in a desired spatial relationship. At least one of these known fasteners has a mounting section with an external thread convolution which engages bone in a vertebra. This known fastener has a retaining section which extends axially outward from the mounting section. An external thread convolution is provided on the retaining section for engagement with an internally threaded element, that is, a nut.
A hexagonal intermediate or head section is provided between the mounting and retaining sections of the known fastener. The intermediate or head section of the known fastener is engageable by a tool to rotate the known fastener relative to a vertebra. A fastener having this construction is disclosed in U.S. Pat. No. 4,854,311. Other known fasteners which are used to retain vertebrae in a desired spatial relationship are disclosed in U.S. Pat. Nos. 5,085,660; 5,257,994; and 5,620,443.